This invention relates to electro-optical character generators for photocomposing apparatus.
It is known, in the art of photocomposing, to provide an array of light sources and to operate individual sources in that array to build up a character on a radiation-sensitive recording medium, such as a film, and to provide relative movements, usually termed set feed and line feed, between the array and the recording medium in order to build up lines of composition. Each character is a conglomeration of elementary areas illuminated by the various selectively operated sources of light.
In order to produce a composition of acceptable typographical quality on the recording medium the elementary areas, and accordingly the effective aperture of the individual sources of light must be very small, for example 0.001 inches or less. A visually clear but not typographically clear image may be obtained from an array of sources of larger effective aperture but the constraint of typographical quality makes the use of arrays which are satisfactory for more display devices unsatisfactory for typographical composition.
Moreover, typographical quality deteriorates unless the light from any particular source or effective source is confined to the area or areas which ought to be illuminated by that source. Various arrangements have been devised to overcome or minimise "cross-talk" between the sources.